Design of Glued Laminated Timber Columns

Abstract

The column design criterion adopted in the 1991 National Design Specification (NDS) contains a parameter c that depends on homogeneity and straightness. The objective of this study was to determine whether the improved homogeneity and initial straightness of laminated members are sufficient to justify a more liberal c -value for glued laminated (glulam) compared with that of solid sawn lumber. For Douglas-fir and southern pine glulam columns of four laminations, laminating did not exert a significant effect on c. For Douglas fir, the most likely value of c was found to be 0.76 (probable range, 0.63–0.89). For southern pine, the most likely value of c was 0.83 (probable range, 0.78–0.87). These values do not differ significantly from the value of c = 0.8 adopted for dimension lumber. Therefore, we conclude that laminating does not exert a significant effect on c in glulam of four laminations. However, the NDS column design criterion is still conservative in the design value for compressive strength parallel to grain.